Conventional vehicles include electric powertrains to increase fuel economy and reduce unwanted gas emissions. Of the vehicles employing electric powetrains there are hybrid electric vehicles (or HEVs), plug-in hybrids (or PHEVs), all-electric vehicles or battery electric vehicles (EVs or BEVs), and fuel cells. The battery packs for these systems typically include an arrangement of 50-250 NiMH or Li-ion battery cells in a confined arrangement. The packs are designed to increase the energy density of each battery cell.
Typically heat dissipation increases with energy density. Battery packs can generate a considerable amount of heat during operation. Moreover, when the ambient temperature is relatively warm thermal control of the battery pack can be difficult. Unwanted heat dissipation can, for example, diminish the energy capacity of the battery pack and affect passenger comfort. Typical operating parameters for the battery pack are within 30 to 40 degrees Celsius. In order to mitigate this, some battery packs are equipped with a cooling system that actively circulates liquid coolant around the battery pack. For example, U.S. Patent Publication No. 2011/0132580 titled “Device for Cooling a Vehicle Battery” discloses a cooling device for a vehicle battery that has a cooling element which provides convective heat transfer from the batteries using fluid ducts. While this method of fluid transfer can be effective, there is a need for improvement with respect to the design of a cooling element in order to increase heat transfer and reduce power demands.
Other systems that actively circulate coolant through a cooling system use expensive refrigerant chillers, thermal expansion valves (or TXVs), or solenoids to cool the battery even under hot ambient conditions. These arrangements require more parts, greater power usage and are typically more expensive than the arrangements discussed herein.
Therefore, it is desirable to have a cooling system for a vehicle battery with improved heat transfer and system costs. It is also desirable to have a method of tailoring the cooling capabilities of the cooling system to meet desired performance demands.